As there is a growing demand for the protection and optimal management of both the surface water and groundwater resources, the understanding of their exchange processes is of great importance. This PhD study aimed at describing the natural spatial and temporal variability of these interactions in lowland catchments, mainly exploring and assessing Distributed Temperature Sensing (DTS) which by detecting variability in temperatures at the Sediment-Water Interface (SWI) can indirectly map variability in groundwater discharge at several spatial and temporal scales.
On the small-scale (<100 m), DTS detected large spatial variability in SWI temperatures with scattered high-discharge sites in a stream and also in a lake where discharge fluxes were estimated by vertical temperature profiles and seepage meter measurements. On the kilometre scale DTS indicated less spatial variability in streambed temperatures but similarly to differential gauging and temperature-based flux estimates, also a heterogeneous discharge pattern with several concentrated discharge sites. Catchment scale variability in groundwater discharge was detected by δ2H and electrical conductivity-based hydrograph separation.
The combination of the different measurements show that DTS was capable of detecting major discharge sites but may mask small-scale heterogeneity in discharge where the traditional point-scale flux estimates give more accurate information about its spatial distribution. Lowland streams can also have soft, mobile streambeds which were shown to influence DTS data by sedimentation and scouring processes. A new methodology was therefore developed for the long-term monitoring of surface water-groundwater exchanges in soft-bedded streams.